Recently, brought on by the shortage in fossil fuel and the ecological consequences of such use, various proposals have been devised for inserting locally generated electrical power into a public utility grid. An assortment of renewable fuel sources have been investigated. The ideal alternative energy fuel source will not have an adverse impact on the ecology and will result in a high grade fuel at a low cost. Common examples of alternative energy fuel sources are wind, hydro, hydrocarbon gas recovery, solar, geothermal and waste heat recovery. Each of these fuel sources may be teamed with electrical power generators.
The difficulty in utilizing these fuel sources lies in the quality of the fuel itself. For example, variations in wind velocity severely limit the usefulness of wind power machines as a steady and constant fuel source for a conventional synchronous or induction generator. This is because conventional generators can deliver usable power only when they operate within a particular speed range. As a result, the wind power machines must employ doubly wound AC generators, or elaborate propeller pitch control and mechanical drive systems that provide appropriate generator speed. To be of practical use, however, doubly-fed systems must provide appropriate rotor excitation and maintain constant stator voltage, which is not easily accomplished. Where high speed geothermal turbines or low speed water wheels are employed, mechanical speed control, reduction, or step-up devices must be used to provide the appropriate rotational speed for AC generation. The efficiency losses which accompany these types of mechanical conversion devices compromise their economic viability and render them generally unsuitable as sources of power.
The compensation provided by these mechanical conversion systems are essential, however, because the insertion of locally generated electrical power into a public utility grid requires exact phase and frequency matching. Accordingly, if a device could be self-synchronizing and tolerant of widely varying rotational speed, the use of alternative fuel sources as a means for generating electricity would be greatly enhanced. One noteworthy example of such a self-synchronizing rotating device can be found in several patents issued to Leo Nickoladze, specifically in U.S. Pat. Nos. 4,701,691 and 4,229,689 which are expressly incorporated herein by reference as though fully set forth.
These latter examples rely on electrical cancellation within the inductive device itself whereby all variations in input power are effectively taken out. An exemplary embodiment of such induction device is shown in FIG. 1. The induction generator of FIG. 1 includes two stages, an exciter stage 10 and a generator stage 12. The exciter stage 10 includes an exciter stator 14 connected to an AC power source 16 and an exciter rotor 18 disposed for rotary advancement by a local power source 19. The generator stage 12 includes a generator rotor 20, connected for common rotation with the exciter rotor 18, and a generator stator 22. The windings of the exciter rotor 18 and the generator rotor 20 are connected together, but wound in opposite directions. The generator stator 22 is connected to a load 23.
In operation, the exciter rotor 18 is rotated by the local power source 19 within the rotating magnetic field developed by the exciter stator 14. The induced signal frequency at the output of the exciter rotor 18 is equal to the summation of the angular rate of the local power source 19 plus the frequency of the AC power source 16. As the generator rotor 20 is rotated within the generator stator 22, the inverse connection to the exciter rotor 14 causes the angular rate produced by the local power source 19 to be subtracted out. The result being an induced voltage at the output of the generating stator 22 equal in rate to the frequency of the AC power source.
While the foregoing Nickoladze solution provides a theoretical output voltage where only the line frequency of the utility grid is produced, in practice, the manufacture of these devices is often fraught with difficulty for three-phase power applications due proper phase angle alignment between the exciter and generator stages and the windings. Often, due to the physical windings of the rotor and stator elements, phase angle alignment between the exciter and generator stages could not be achieved in the past. Moreover, some devices simply failed to perform altogether because the phase sequence of the windings was improper. These problems become even more pronounced when the exciter stage and generator stage are manufactured independently of one another.
Accordingly, there is a current need for a three-phase line synchronous generator that can be produced with proper phase angle alignment for three-phase power applications resulting in a constant frequency and voltage output at variable shaft speeds. It is desirable that phase angle alignment be easily achieved even for exciter and generator components wound in opposite directions or with phases that start in different slots on the core with relation to the keyway.